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I skipped a lot of the afternoon presentations at XTech to spend some time in the Dublin sunshine. I came back to attend Blaine’s presentation on The Real Time Web only to find that Blaine and Maureen didn’t make it over to Ireland because of visa technicalities. That’s a shame. But Matt is stepping into the breach. He has taken Blaine’s slides and assembled a panel with Seth and Rabble from Fire Eagle to answer the questions raised by Blaine.

Matt poses the first question …what is the real-time Web? Rabble says that HTTP lets us load data but isn’t so good at realtime two-way interaction. Seth concurs. With HTTP you have to poll “has anything changed? has anything changed? has anything changed?” As Rabble says, this doesn’t scale very well. With Jabber there is only one connection request and one response and that response is sent when something has changed.

What’s wrong with HTTP, Comet or SMTP? Seth says that SMTP has no verifiable authentication and there’s no consistent API. Rabble says that pinging with HTTP has timeout problems. Seth says that Comet is a nice hack (or family of hacks, as Matt says) but it doesn’t scale. Bollocks! says Simon, Meebo!

Jabber has a lot of confusing documentation. What’s the state of play for the modern programmer? Rabble dives in. Jabber is just streaming XML documents and the specs tell you what to expect in that stream. Jabber addressing looks a lot like emails. Seth explains the federation aspect. Jabber servers authenticate with each other. The payload, like with email, is a message, explains Rabble. Apart from the basic body of the message, you can include other things like attachments. Seth points out that you can get presence information like whether a mobile device is on roaming. You can subscribe to Jabber nodes so that you receive notifications of change from that node. Matt makes the observation that at this point we’re talking about a lot more than just delivering documents.

So we can send and receive messages from either end, says Matt. There’s a sense of a “roster”: end points that you can send and receive data from. That sounds fine for IM but what happens when you apply this to applications? Twitter and Dopplr can both be operated from a chat client. Matt says that this is a great way to structure an API.

Rabble says that everything old is new again. Twitter, the poster child of the new Web, is applying the concept of IRC channels.

Matt asks Rabble to explain how this works with Fire Eagle. Rabble says that Fire Eagle is a fairly simple app but even a simple HTTP client will ping it a lot because they want to get updated location data quickly. With a subscribable end point that represents a user, you get a relatively real-time update of someone’s location.

What about state? The persistence of state in IM is what allows conversations. What are the gotchas of dealing with state?

Well, says Seth, you don’t have a consistent API. Rabble says there is SOAP over XMPP …the room chuckles. The biggest gotcha, says Seth, is XMPP’s heritage as a chat server. You will have a lot of connections.

Chat clients are good interfaces for humans. Twitter goes further and sends back the human-readable message but also a machine-readable description of the message. Are there design challenges in building this kind of thing?

Rabble says the first thing is to always include a body, the human-readable message. Then you can overload that with plenty of data formats; all the usual suspects. GEO Atom in FIre Eagle, for example.

Matt asks them to explain PubSup. It’s Publish/Subscribe, says Seth. Rather than a one-to-one interaction, you send a PubSub request to a particular node and then get back a stream of updates. In Twitter, for example, you can get a stream of the public timeline by subscribing to a node. Rabble mentions Ralph and Blaine’s Twitter/Jaiku bridge that they hacked together during one night at Social Graph Foo Camp. Seth says you can also filter the streams. Matt points out that this is what Tweetscan does now. They used to ping a lot but know they just subscribe. Rabble wonders if we can handle all of this activity. There’s just so much stuff coming back. With RSS we have tricks like “last modified” timestamps and etags but it would be so much easier if every blog had a subscribable node.

We welcome to the stage a special guest, it’s Ralph. Matt introduces the story of the all-night hackathon from Social Graph Foo Camp and asks Ralph to tell us what happened there. Ralph had two chat windows open: one for the Twitterbot, one for the Jaikubot. They hacked and hacked all night. Data was flowing from the US (Twitter) to Europe (Jaiku) and in the other direction. At 7:10am in Sebastapol one chat window went “ping!” and one and a half seconds later another chat window went “pong!”

Matt asks Ralph to stay on the panel for questions. The questions come thick and fast from Dan, Dave, Simon and Gavin. The answers come even faster. I can’t keep up with liveblogging this — always a good sign. You kind of had to be there.